This project is an investigation into the radiative properties of ice crystals in the polar atmosphere, and an assessment how these crystals affect radiative fluxes, local heating rates, and visibility. Ice crystals have not generally been considered important in the polar atmosphere, primarily because attention was focussed on anthropogenic pollutants, and few optical effects such as those associated with mid- latitude cirrus clouds have been observed. However in the antarctic atmosphere, clear-sky ice crystal precipitation has consistently been observed, and at interior stations can account for more than 80 percent of the annual precipitation. Optical effects, including some quite rare ones, due to ice crystals are observed frequently at South Pole Station. The climatology of arctic ice crystal is much less certain. Observations of ice crystals in the arctic from both the surface and from satellites is difficult, particularly during the polar night. The occurrence of ice crystals may be noted in the synoptic present weather code, but more likely will not be noted at all. Satellite observation of ice crystals, particularly over a snow or ice surface, or in the polar night, remains an unsolved problem. Recently however this question has become more prominent as evidence is accumulating that the horizontal visibility in arctic haze events is significantly less than would be expected from the scattering characteristics of the haze particles alone, and a significant ice crystal concentrations seem to be indicated. This project will develop a cloud microphysics parameterization scheme, based on observations of ice crystals, chemistry, and meteorological conditions to be made in March and April 1989. The model output of the radiative flux divergences and heating rates will be coupled to a thermodynamic sea ice model which will in turn provide equilibrium sea ice thickness values. This will provide a unique and innovative look at how ice crystals interact with the chemical, dynamical and radiative processes in the polar atmosphere.
